The present invention relates to a structure for mounting a rotary code disk on a rotary shaft of an optical encoder for use in combination with a servomotor, a machine tool or a measuring apparatus.
FIG. 4A is a schematic sectional view of a conventional rotary code disk mounting structure, FIG. 4B is an enlarged sectional view of an essential portion of the same rotary code disk mounting structure, and FIG. 4C is an exploded perspective view of the same rotary code disk mounting structure. Referring to FIGS. 4A, 4B and 4C, when mounting rotary code disk 3 made from 3 mm thick glass and having a central hole 30 on a spindle 2, the rotary code disk 3 is placed on the lapped support surface 20 of the spindle 2, a ring 4 is put on the head 25 of the spindle 2 projecting through the central hole 30 of the code disk 3, the ring 4 is depressed with a jig so that the tongues 41 of the ring 4 are bent to fasten the code disk 3 temporarily on the support surface 20, the code disk 3 is centered with a microscope while the spindle 2 is rotated, and then the ring 4 is buried in an adhesive J to fasten the code disk 3 to the spindle 2.
This conventional rotary code disk mounting structure fastens the code disk 3 to the spindle 2 by bonding a portion of the upper surface of the code disk 3 around the central hole 30 and the outer circumference of the projecting head 25 with the adhesive J. Therefore, the diameter D.sub.0 of the head 25 must be comparatively large to secure a desired fastening strength, and thus the diameter of the center hole 30 of the code disk 3 must be comparatively large. The center hole 30 reduces the impact strength of the glass code disk 3, and thus the code disk 3 provided with the center hole 30 must be comparatively thick. Furthermore, the code disk 3 provided with the center hole 30 requires an additional process for forming the center hole 30.
The present invention is intended to eliminate the foregoing disadvantages by employing a novel mounting structure.